In recent years, a display device having a function of showing a space behind a display screen transparently (hereinafter referred to as a see-through type display device) has been developed. The see-through type display device is also called a transparent display or a see-through display. For example, a see-through type liquid crystal display device can be constituted by disposing, behind a liquid crystal panel, an edge light type backlight having a transparent light guide plate. In the see-through type liquid crystal display device constituted like this, when the backlight is turned off and transmittance of pixels in the liquid crystal panel is controlled to be high, a space behind the liquid crystal panel can be seen transparently. Patent Document 1 discloses a see-through type liquid crystal display device having a shutter film disposed behind a liquid crystal panel. Furthermore, a see-through type organic electro-luminescence (hereinafter referred to as EL) display device having a transparent pixel electrode has also been developed.
The see-through type display device is placed and used in a public facility, a commercial facility, an amusement machine, or the like. According to the see-through type display device, the space behind the display screen can be seen transparently when a video is not displayed. The see-through type display device has an advantage that the device blends into surrounding circumstances and does not hinder a vision.
Relating to the present invention, Patent Document 2 discloses determining transparency of display based on a passing time from last used time of a window, when performing multi-window display.